This invention relates to an essentially scrap free process for forming articles directly from powders of normally solid thermoplastic polymers.
Recently there has been discovered and described in application Ser. No. 215,632 filed Jan. 5, 1972, now abandoned, a new and useful process for forming articles directly from powdered thermoplastic resin materials. It has been found that plastic articles can be made in this manner at lesser expense than comparable articles made by either injection molding or conventional vacuum forming processes. The favorable economics of this newly described powder forming process are realized as a result of eliminating a pelletizing step, eliminating the formation of scrap, reducing the cooling cycle, and utilizing the polymer powder more efficiently.
In the practice of the aforementioned disclosed process, it is desirable, if not essential, to heat the briquettes prior to forging in order to cause at least partial sintering of the resin particles of the briquettes. This sintering is usually done in order to increase the cohesiveness or bond strength between the resin particles of the briquette so that it can be readily handled in preparation for forging and then forged satisfactorily. In addition, articles prepared by this technique often contain voids or areas of incomplete fusion in the molded plastic, hereinafter called "foam spots" unless special precautions are taken.
In order to achieve more favorable economics in the practice of the aforementioned powder forming process, it would be highly desirable to provide an improved process which substantially reduces the time of sintering the briquettes of the thermoplastic resinous polymer powder and which eliminates the formation of foam spots in the resultant articles.